1. Field of the Invention
This invention relates to the combustion of gaseous fuels and more particularly to the mixing of gaseous fuels with air and with products of combustion within a burner such as is used for the direct-fired heating of an airstream.
2. Description of the Prior Art
One of the problems and disadvantages of gas fired air heaters is that many of them are indirectly fired and therefore waste a large amount of heat which goes up the exhaust stack from the combustion chamber. In such indirectly fired heaters, the gas is burned within a combustion chamber which has metal walls and functions as a heater exchanger. The airstream to be heated is blown around these walls and heat exchanging surfaces and thus absorbs the heat therefrom. In this type of indirectly fired heater, the products of combustion, which might be noxious or irritating, are kept out of the airstream to be heated. While this does accomplish a great degree of safety, it does waste a lot of heat.
Where large volumes of air are to be heated and where the presence of products of combustion is not objectionable, the direct-fired type air heaters are used. In these heaters, the gas burners are simply placed in the airstream, and the products of combustion mix with the airstream. This type of heater finds application as makeup air heaters for large factories, crop driers, and for other type industrial drying purposes. Direct gas-fired air heaters do not waste much heat, but many of them do not mix the air with the incoming gaseous fuel as well as they should, and therefore the combustion is somewhat inefficient, as well as being more of a pollutant and safety hazard.
Direct gas-fired air heaters are generally of two types, premix and non-premix types. In the premix type, the gaseous fuel is mixed with primary combustion air and this mixture is blown into the burners for combustion. In burners of the non-premix type, the gaseous fuel is piped directly to the burner head where is is then mixed with a portion of the airstream, and this combustible mixture is then burned in the airstream.
Non-premix burner heads take a variety of forms, but the type which has a flame holder made of perforated metal, of some high temperature resistant material, contains the flame and creates the turbulence desired for mixing the combustion air with the gaseous fuel. Burners of this type usually have a plurality of small orifices so that the pressurized gas fuel enters the burner in a plurality of small jet streams which provide additional turbulent mixing and more efficient combustion of the fuel. When applying such a burner under conditions of different airstream volumes, or of different type fuel gases, such as butane or natural gas, it is often necessary to change the orifice size in order to maintain efficient operation. This not only involves a considerable amount of labor, but also necessitates having the desired size orifices at hand. Labor being as costly as it is today, this expense can be quite great, while keeping an inventory of different orifices on hand also can be fairly costly. Furthermore, keeping track of the supply of orifices requires further manpower and expense.
Known prior art patents which may be pertinent to this invention are listed as follows:
______________________________________ 794,225 A. H. Humphrey July 11, 1905 1,739,515 J. F. Mustee Dec. 17, 1929 1,766,803 A. A. Scott et al June 24, 1930 2,044,953 H. R. Palmer June 23, 1936 3,820,945 Roger Vignes June 28, 1974 ______________________________________
None of the known devices teaches the new and novel structure as disclosed by the invention herein.